In situ embedding of cobalt sulfide quantum dots among transition metal layered double hydroxides for high performance all-solid-state asymmetric supercapacitors

Abstract

Layered double hydroxides (LDHs) are widely used as cathode materials for supercapacitors (SCs), thanks to their many advantages. However, the single metal species with limited active sites limit the further improvement of the electrochemical performance of LDH materials. We successfully in situ embedded cobalt sulfide quantum dots (Co₉S₈-QDs) between the layers of ternary metal LDHs derived from metal–organic-frameworks (MOFs) by selective vulcanization of Co. The prepared Ni₃Mn₁Co@Co₉S₈-QDs/NF nanocomposites retain the advantages of LDH materials, such as lower charge transfer resistance. At the same time, the selectively generated ultra-small sized Co₉S₈-QDs reveal more active sites, which complies with the size minimization strategy, leading to the largely enhanced electrochemical properties. Due to the cooperative effect of LDHs and Co₉S₈-QDs, the prepared electrode has an excellent capacity (492.1 mA h g⁻¹ at 1 A g⁻¹), remarkable equivalent series resistance (0.499 Ω) and superior capacity retention (90.4% after 10 000 charge–discharge cycles). In addition, the carbon coated Fe₂O₃ nanoarray is prepared on carbon cloth (CC) as the cathode electrode (Fe₂O₃@C/CC), and the prepared Ni₃Mn₁Co@Co₉S₈-QDs/NF//Fe₂O₃@C/CC all solid-state asymmetric supercapacitor (ASC) shows an outstanding energy density (71.48 W h kg⁻¹) when the power density is 750 W kg⁻¹ and excellent capacity retention (93.7% after 10 000 charge–discharge cycles). As a result, the construction of composite electrodes with polymetallic LDHs and in situ embedded quantum dots should envision broad prospects.